Nick Pugh wrote:
> Yes the tones are clean and not distorted. The high tone is about 6 db
> lower in amplitude the low frequency tone.
>> nick
> ----- Original Message ----- From: "Ray Wells" <vk2tv at exemail.com.au>
> To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
> Sent: Friday, August 31, 2007 4:15 PM
> Subject: Re: [aprssig] paccom schematic
>>>> Nick Pugh wrote:
>>>>> I have a Pacomm Picopacket It will tx ox but is decoding 1 out of 4
>>> rx packets The input level is set to about 300 mv pp
>>> does the group have any suggestions??
>>> nick
>>>>>> ------------------------------------------------------------------------
>>>>>>>>> _______________________________________________
>>> aprssig mailing list
>>>aprssig at lists.tapr.org>>>https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig>>>>> Have you looked at the audio to the TNC with a CRO to see what the
>> tones look like? That's the first thing I would do.
>>>> Ray vk2tv
>>>> _______________________________________________
>> aprssig mailing list
>>aprssig at lists.tapr.org>>https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig>>>> _______________________________________________
> aprssig mailing list
>aprssig at lists.tapr.org>https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig>Hi Nick,
You've just discovered your problem. The tones must be the same
amplitude going to the TNC, or very close to it.
Some modem chips are particularly non-cooperative when the high tone is
lower in amplitude than the low tone.
I wonder where you're getting the audio from in the radio?
The usual sequence is that tones of equal amplitude are fed into the
transmitter. Pre-emphasis cause the high tone to be approximately 6dB
higher than the low tone when transmitted. At the other end, de-emphasis
in the rx restores the tones to equal amplitude to go to the TNC.
Causes?
1. No pre-emphasis at the tx
2. Your rx is applying additional "slope" at the point you're grabbing
the audio.
My first attempt at packet was using a Multi 750 2m rig and for
convenience I grabbed speaker audio and had exactly your problem. The
high tone at the speaker was about 8dB down on the low tone.
You obviously have a CRO so start looking around the rx for a point that
provides flat audio.
Ray vk2tv